The skin is the body's largest organ, covering about 1.5-2 square metres and making up roughly 15% of body weight in adults. It has two main layers, the outer epidermis and the deeper dermis, resting on the subcutaneous fat of the hypodermis. Together with its hair, nails and glands it forms the integumentary system.
| Location | Covers the entire external surface of the body, continuous with the mucous membranes at the body openings |
|---|---|
| Parts |
|
| Nerve Supply | Cutaneous branches of the spinal and cranial nerves (sensory); Postganglionic sympathetic fibres (blood vessels, sweat glands, arrector pili) |
| Blood Supply | Direct cutaneous arteries; Musculocutaneous and fasciocutaneous perforator arteries; Subdermal and subpapillary arterial plexuses |
| Venous drainage |
|
| Lymphatic drainage |
|
Protects against injury, microbes and ultraviolet light, prevents water loss, regulates temperature, senses touch, pain and temperature, and makes vitamin D.
Skin is the first barrier against infection, ultraviolet light, water loss and injury, so its breakdown (burns, ulcers, wounds) quickly causes dehydration and infection. Skin cancers are the most common cancers; basal cell carcinoma is the most frequent, while melanoma is the most dangerous. Pressure injuries develop over bony points such as the sacrum and heels when skin is compressed for long periods. Skin colour, temperature and turgor give quick clinical clues to circulation, oxygenation and hydration.
Damage to skin by heat, chemicals, electricity or radiation, graded by depth from superficial to full thickness.
Breakdown of skin and deeper tissue over bony prominences from sustained pressure, common in immobile people.
Basal cell carcinoma, squamous cell carcinoma and melanoma, strongly linked to ultraviolet exposure.
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